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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>onmouseover事件</title>
    <script>
        function writeText(txt) {
            document.getElementById("desc").innerHTML = txt;
        }
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    <img src="planets.gif" width="145" height="126" alt="Planets" usemap="#planetmap" />
    <map name="planetmap">
        <area shape="rect" coords="0,0,82,126" onmouseover="writeText('太阳和气体巨星类似木星是太阳系中最大的物体。')" href="sun.htm"
            target="_blank" alt="Sun" />
        <area shape="circle" coords="90,58,3" onmouseover="writeText('从地球上很难研究水星，因为它太接近太阳。')" href="mercur.htm"
            target="_blank" alt="Mercury" />
        <area shape="circle" coords="124,58,8"
            onmouseover="writeText('至到1960年，金星经常被认为是地球的孪生妹妹，因为金星是最靠近我们的行星，并且两个行星有很多相似的特点。')" t')" href="venus.htm"
            target="_blank" alt="Venus" />
    </map>
    <p id="desc">鼠标在太阳和星星上移动，可以看到不同的描述。</p>
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